At least 40 rights workers, activists and lawyers have been rounded up by Egyptian authorities since late October and are being held in "unknown places," Human Rights Watch (HRW) has said, calling on the authorities to reveal their whereabouts.

"Many of those arrested were providing legal and humanitarian support to families of political detainees," who were also reported missing after their arrest, the rights group said in a statement on Sunday.

HRW said it had spoken to "a lawyer, a human rights activist and two political activists who have been in direct contact with the families of those arrested" since the end of October.

"The crackdown on Egyptian security agencies is now affecting ... those brave men and women who have tried to protect the missing," said Michael Page, deputy director of HRW Middle East.

One of the sources consulted by HRW reported at least 80 disappearances since the end of October, but only 40 have been "verified" by the organisation.

"The Egyptian authorities should immediately reveal the place of detention of prisoners, release all those arrested only for exercising their rights, and bring before a judge the others to consider their detention," said the rights group.

Sources told HRW that some of the detainees were close to the Egyptian Coordination for Rights and Freedoms, an independent human rights group it said has come under fire from pro-government media in recent months, the AFP news agency reported.

'They blindfolded her'

Among those detained are Hoda Abdelmoneim, a 60-year-old lawyer and former spokesperson for the Revolutionary Coalition of Egyptian Women, a group close to the Muslim Brotherhood.

Fadwa Khaled, Abdelmoneim's eldest daughter, was the only one at home when her mother was arrested on 1 November in Cairo.

"She was sleeping, but I was awake when, at 1.30am, the door of our flat was broken, and nearly 20 officers stormed the flat," she told Middle East Eye.

"They blindfolded her and refused to let her take any of her belongings or medication.

"They did not allow me any contact with her or to say goodbye."

Aisha Khairat al-Shater, the daughter of one of the leaders of the Muslim Brotherhood who is currently detained, was also arrested, as was her husband, lawyer Mohamed Abou Horayra.